Exposure of a light-sensitive printing plate precursor through an original has conventionally been conducted by disposing a light-sensitive printing plate precursor and an original in a superposed state between a rubber sheet and a pressure glass, and evacuating the interface between the rubber sheet and the pressure glass to completely contact the original with the surface of the light-sensitive layer of the light-sensitive printing plate precursor.
In order to shorten the vacuum-contacting time, there is known a light-sensitive printing plate precursor having micro-patterns consisting of coated portions and non-coated portions on the light-sensitive layer prepared according to the process described in, for example, U.S. Pat. No. 4,216,289.
Recent requirements for saving resources have promoted the spread of double-coated light-sensitive printing plate precursors. However, in the case of providing micro-patterns on both light-sensitive layer surfaces of such type light-sensitive printing plate precursor according to the above-described process, the micro-patterns must be first coated on one side of the plate precursor and dried, then on the other side of the plate precursor, and thus considerably large-scale equipment is required. In addition, the coated portions of the micro-patterns provided on the back side according to the above-described process are often delaminated or crushed before the step of being cut into a desired size due to rubbing by conveyor rollers, resulting in a longer vacuum-contacting time upon imagewise exposure of the light-sensitive layer on the back side as compared with the exposure on the surface. Also, in the exposure step, the coated portions of the micro-patters on the back side to be exposed layer are sometimes pressed and crushed by a printer upon vacuum exposure of the surface, resulting in a prolonged evacuation upon exposure of the back side.
Japanese Patent Application (OPI) No. 98505/76 (the term "OPI" as used herein refers to a "published unexamined Japanese Patent Application") discloses a process for coating a dispersion of waxy or fine-powdered resin having release properties in a low-boiling organic solvent by air-spraying to thereby solve the problem that the coating for improving the vacuum contact properties stains a film original. However, this spary-coated layer is liable to be delaminated due to weak adhesion force for the surface of the light-sensitive printing plate precursor, thus also causing the above-described problem. In addition, the use of an organic solvent is not favorable from the viewpoint of safety during production of the printing plate precursor.
British Pat. No. GB2,025,646A discloses a process of powdering solid powder and thermally fixing it on a light-sensitive printing plate precursor. With double-coated light-sensitive printing plates precursors, however, the mat layer on one side is likely to be crushed during roller conveying before being cooled after the thermowelding. Conveying without using rollers involves handling difficulties. Further, preparation of powder requires pulverization and classification of a resin, leading to high production costs.